Neutral lubricity-increasing agents



Patented Mar. 23, 1943 I Arthur w. Burwell, Niagara Falls, N. Y., assignor to Alex Corporation, New York, N. Y., a corporation of New York No Drawing. Application June 7,1941,

' Serial No. 397,137

4 Claims. (chase-42) This invention relates to the art of improving.

the lubricating properties of a mineral lubricating oil by the incorporation thereinto of a'relatively small amount of an oil-soluble lubricity.-

increasing agent, and is particularly concerned with the problem of insuring the neutralityv of such an agent and of the compounded lubricating oil of which it is a part.

U. S. Patent No. 2,096,390 to Arthur W. Burwell and Adolf Kempe describes the preparation of such a lubricity-increasing agent by esterifying with a lower molecular weight aliphatic alcohol (e. g., methyl alcohol, ethyl alcohol, or the like) or equivalent esterifying agent the esterifiable components of a mixturerich in or consisting essentially of relatively high molecular weight In my researches to overcome the occasionally low solubility characteristics of the neutralized esters mixtures I found that the substitution of a basically-reacting compound of sodium or potassium for the basically-reacting compound of calcium as neutralizing agent improves the solubility characteristics of the resulting products, making-same at least as oil-soluble as are the parent esters mixtures. However, it has been demonstrated that decomposition products of the sodium (or potassium) salts are or may be distinctly harmful to engine parts containing aluminum or magnesium or an alloy of aluminum or magnesium; therefore, the use of esters mixsaturated aliphatic carboxylic acids (hereinafter referred to as petroleum acids)-of oxygenated compounds produced by the liquid phase con trolled, partial oxidation of a mixture of hydrocarbons of mineral origin. The resulting ester mixtures, or ester-rich mixtures, are added to lubricating oils of various sorts in amounts ranging between about 0.25% and about 2% (or even .up to 4% or 6%) by weight.

I found that the above described esters mixtures show a persistent although slight acidity (e. g., equivalent to an acid number of the order of 14 to, say, 8), and in copending application Serial No. 362,658, filed October 24, 1940, I have described and claimed the concept of reducing such residual acidity by treating the esters mixture, or the esters-rich mixture, with a basically reacting compound of an alkaline metal (e. g.',

of calcium) whereby to convert the mixtures small content of free petroleum acids into the corresponding alkaline earth metal (e. g., calcium) salts. The resulting lubricity-increasing agent consists essentially of a mixture of esters .of petroleum acids associated with a relatively very small amount of calcium salts of the petroleum acids, and is either completely neutral or substantially so. Where the oil-solubility characteristics of the calcium salts-containing agent are not inimical to such use, the product when dissolved in a lubricating oil improves the functioning of the latter without increasing its acidity. However, I have found that the calcium salts-containing esters mixtures are, in some cases, somewhat less completely soluble than are the esters mixtures before neutralization, and that in some instances the calcium salts-containing esters mixtures are unavailable as lubricity-increasing agents by reason of this decrease in oil-solubility.

tures neutralized with a basically reacting compound of sodium (or potassium) is or might be prejudicial in the lubrication of engine parts containing said metals.

I have now found that the above disadvantages may be avoided, and that certain independent advantages may be gained, by neutralizing the aforesaid esters mixtures with a basically-reacting compound of lithium (e. g., with lithium hydroxide or lithium oxide or lithium carbonate) in lieu of calcium compounds or sodium (or potassium) compounds heretofore suggested. The resulting lithium salts-containing, neutral, esters mixture are harmless to engine parts containing aluminum or magnesium or an alloy of aluminum or magnesium; moreover, they have outstandingly good solubility properties with respect to lubricating oils of all sorts and of all viscosities, being completely soluble not only in oils of the character of lubricating oils but also even in such light hydrocarbon mixtures as gasoline. The lithium soaps .,do not (in the quantities encountered in the carrying out of the present invention) form gels, as do the corresponding sodium and potassium soaps in corresponding quantity. Less lithium compound is required, to efiect neutrality, than calcium compound (or sodium, or potassium, compound) because of the lower molecular weight of the former. I find, too, that use of lithium hydroxide (or other reactive compound of lithium) serves effectually to neutralize the last traces of acidity in the esters mixtures. And, moreover, inclusion in the esters mixtures of a small amount of petroleum acid salts of lithium provides a more ready and sure identification of my product than does inclusion of the corresponding calcium or sodium or potassium salts, since it is a. fact that a simple and easily performed flame test positively will' discover the presence of a mere trace of the lithium salts in a compounded lubricating oil whereas the same test is much less conclusive in the cases of calcium salts and sodium (or potassium) salts.

For neutralizing the aforesaid free acids-containing esters mixture I prefer--although the same is not essentialto treat the latter with lithium hydroxide in alcoholic solution, in amount sutficient to effect complete neutralization of the residual free acids, and thereafter to remove the alcohol and reaction water from the so-treated esters mixture by heating the latter to dehydration temperature (e. g., by distillation at between 212 F. and about 250 F.) for some time. Use of alcohol as solvent for the lithium hydroxide has the advantage that the alcohol greatly aids in dispersion of the lithium hydroxide through the ester mixture. In place of the alcohol I may use another relatively readily volatile organic solvent for the lithium compound which organic solvent is chemically inert to the lithium compound and to the ester mixture under the conditions of use.

In the alternative, I may neutralise the aforesaid free acids-containing esters mixture by treating the latter, which was a commercial aqueous lithium hydroxide product showing an LiOH content of 54%, balance mostly water. It wa determined that the amount of this commercial LiOH product necessary to just neutralize the acids present in 200 grams of the esters mixture was 1.047 grams.

Four samples, of 200 grams each, of the esters mixture were warmed to from about 120 to 'about 150 F. (this being just suflicient to melt the esters mixture) and to them varying amounts (noted below) of the commercial LiOH product were added, with thorough stirring for from onehalf to three-quarters of an hour. The temperature of the samples was raised quickly to about 230--250 F. and there maintained until all water had been removed. The results were as follows:

323? fig Times equivalent Acid number 0.833 gram Below equivalent.-- 2.5. 1.0400 grams Equivalent 1.8. M3060 grams 1.5 times equivalent. Reacts alkaline. 2.4900 grams 2.5 times equivalent. Do.

neutralizing mixtures consisting essentially of esters of petroleum acids with a reactive compound of lithium is not limited to the hereinbefore referred to methyl esters mixture, but rather is applicable generally to mixtures containing or consisting essentially of alkyl esters of petroleum acids. Also, it is to be appreciated that lithium carbonate or lithium oxide may be employed,- instead of lithium hydroxide, as the reactive compound of lithium.

I claim:

1. Process of improving the utility for use in lubricating oil compositions of a mixture consisting essentially of low molecular weight aliphatic alcohol esters of relatively high molecular weight saturated aliphatic carboxylic acids of mineral origin and a minor proportion of the unesterified acids, which comprises treating the mixture with a reactive compound of lithium in an amount at least substantially equivalent to the acid number of the mixture, and heating the so-treated mixture to dehydrating temperature.

2. Process of improving the utility for use in lubricating oil compositions of a mixture consisting essentially of low molecular weight aliphatic alcohol esters of relatively high molecular weight saturated aliphatic carboxylic acids of mineral origin and containing a minor proportion of the unesterified acids, which comprises treating such ester mixture with a solution of a reactive compound of lithium in a readily volatile organic solvent therefor which solvent is chemically inert both to the lithium compound and to the ester mixture, the lithium compound being added in an amount at least substantially equivalent to the acid number of the ester mixture, and heating the so-treated mixture to dehydrating temperature.

3. Process which comprises treating a mixture consisting essentially of alkyl esters of relatively high molecular weight saturated aliphatic carboxylic acids of low acid number with lithium hydroxide in an amount at least substantially equivalent to the acid number of the ester mixture and heating the so-treated mixture to dehydrating temperature.

4. An improved lubricity-increasing agent for use in lubricating oils consisting essentially of a mixture of low molecular weight aliphatic alcohol esters of relatively high molecular weight saturated aliphatic carboxylic acids of mineral origin and a minor proportion oi lithium soaps of saidacids, the acid number of said mixture not exceeding 2, said mix-ture being characterized by being substantially non-corrosive to aluminum, magnesium and alloys thereof.

ARTHUR W. BURWELL. 

